The alarm reaction consists of an elaborate chain of biochemical

The alarm reaction consists of an elaborate chain of biochemical and structural alterations occurring in an organism exposed to sudden and intense stimulus situations. These stimulus situations may be of a symbolic nature: or they may consist of injury of the brain or spinal cord such as in physical trauma; or they may consist of conditions producing more generalized effects, as, for example, burns, hemorrhage, obstetrical surgery, muscular exercise, emotionally traumatic situations, and exposure to cold or burns: or they may be of a systemic nature, such as infectious diseases, drugs, bacterial toxins, anoxia, X rays, radium rays, or solar rays. Appropriate behavior to alleviate the stress can be displayed by the individual to some of the stimulus situations which produce the alarm reaction. This is especially true if the threat to the individual is on a symbolic level. Those traumatic stimulus situations which allow behavioral mechanisms to alleviate the condition can be considered as exogenous. On the other hand. appropriate behavior to dispel a situation such as an infection or toxin cannot be exhibited. These conditions can be considered as endogenous.

The remarkable fact about the alarm reaction is that, irrespective of the wide variety of different stimuli which will elicit it, the complex internal changes are similar. This means that the physiological disturbance is not specific to the conditions producing it but consists of a generalized systemic reaction. These facts are in conformity with what has already been pointed out to the effect that under emotional duress the homeostasis of the body is generally disturbed.

Part of the alarm reaction consists of signs of damage and shock to the organism. At the same time or immediately following the first reaction to shock, the drive to reinstate homeostasis is initiated and mechanisms are thrown into function as a defense against the shock. The alarm reaction can then be divided into two phases, the initial shock and the countershock. The latter consists largely of the defense reactions following immediately after shock. In this respect fatigue produced by muscular exercise differs from many of the other traumatic stimulus situations producing shock in that it causes little shock but introduces physiological reactions to counteract the conditions of fatigue.

There is no clear demarcation between the shock and countershock phases of the alarm reaction. During the shock phase changes occur in the circulatory system, such as a more rapid pulse, a slight increase of blood pressure followed by pronounced hypotension, and a constriction of the peripheral arteries. Very extensive changes in the blood content also take place. In the first place the fluid of the blood is lost and a greater concentration of the blood plasma is present, with a decrease of the blood volume. This is not due to excretion of the fluid through the kidneys, because micturition is held in abeyance during shock, but because of the infiltration of the fluid into the tissues of the body. A rapid diminution in circulation time occurs. At the same time there is a slight rise followed by a fall of the blood sugar level. The white and red cell counts increase. The pH of the blood may change in the direction of acidity. A decrease of the blood chlorides is one of the most constant findings in the shock reaction. Other changes in the blood are a decrease of the cholesterol content, derangement of the nitrogen metabolism as shown by the increase of nonprotein nitrogen and an increase in the potassium and phosphate content. Epinephrine, the hormone of the medulla of the adrenal glands, is found in the blood stream. The blood coagulates more rapidly, since fibrin, the essential portion of the blood clot, is formed more rapidly. During this phase the general metabolism of the body will decrease, the body temperature will fall, and the tonicity of the muscles will be decreased. Morphological changes such as that involving the lymphatic organs and the gastrointestinal tract will be initiated and continued through the countershock phase. As pointed out, these reactions can be considered largely as direct signs produced by the traumatic situation, although some of them, such as the increase in the white and red blood cells, may be considered as protective mechanisms.

The countershock phase of the alarm reaction which follows immediately after the shock phase consists largely of homeostatic mechanisms thrown into function to cope with the effects of shock, in addition to the morphological changes initiated by the shock. For this reason many of the biochemical and physiological changes during this phase are reversed. The body temperature increases and may result in fever. The blood pressure and basal metabolism increase and may be raised above normal. The blood stream becomes more diluted and micturition will be frequent. The blood sugar and the blood chlorides rise to their normal levels or higher. The blood may become more alkaline. Morphological changes started during the shock phase may continue or become exaggerated. Gastrointestinal ulcerations are present. The thymus, the lymph nodes, the spleen, and other lymphatic organs, as well as the pancreas, decrease in size and may show degenerative changes. This may occur in the medulla of the adrenal gland as well as in the thyroid and the liver. The liver may become infiltrated with fatty tissue. A depressing effect is produced on growth and gonadal activity. On the other hand the cortex of the adrenal gland increases in size and is stimulated to hypersecretion. The anterior lobe of the hypophysis, at least in some animals such as the rat, also becomes hypertrophic, although in some experiments this result has not been obtained.

The alarm reaction usually occurs immediately upon the application of the traumatic stimulus, although many of the disturbances may appear in the next 24 hours. The alarm reaction is followed by the stage of resistance. By the stage of resistance is meant that the organism builds up a capacity to withstand the effects of a specific stress to which it is repeatedly exposed. For example, an animal exposed to a very cold environment will first show the alarm reaction. If repeatedly exposed to the cold over a number of days, it builds up a resistance to exposure. This result holds true for all the other stimulus situations capable of producing the alarm reaction. The stage of resistance means that the homeostatic mechanisms are thrown into function to cope with a specific disturbing stimulus situation in order to alleviate its physiological effects. If such stimulation is continued, however, the resistance of the organism finally breaks down. The stage of exhaustion is reached, and death is the final outcome. The period of resistance may last for a few weeks or months, depending upon the nature of the stress, its intensity, and the frequency of application.

During the period of resistance most of the symptoms concomitant with the alarm reaction disappear and resistance to the damaging stimulus is acquired. The biochemical processes return to normal and in some cases may even be reversed; for example, there may be an increase in blood chlorides. The gastrointestinal ulcers recede, as do some of the other morphological changes, such as those involving the thymus and the other lymphatic organs. However, the gonads may continue to show atrophy. Growth is not normal. The lactating female stops producing milk. The cells of the thyroid may proliferate during this period. Thickening of the walls of the arteries, formation of fibrous nodules in the heart, and other cardiovascular lesions may occur, but only under special predisposing conditions such as a high sodium and protein diet and further sensitizing of the animal by the removal of one of the kidneys. These same additional factors may produce organic changes in the glomerular capillaries of the kidney and even inflammation of the kidneys. If the kidneys are involved, blood pressure will be elevated. Lesions of the joints may also appear.

If an organism is continually exposed to a stress, it builds up a resistance to that specific stimulus situation. However, at the same time it becomes less resistant to other traumatic stimuli. During the stage of resistance, adaptation to one traumatic stimulus situation is acquired at the expense of the ability to withstand other stresses which may occur. During the shock phase of the alarm reaction general resistance is lowered to both the specific stress and extraneous stresses. During the countershock phase a resistance is present to all traumatic stimuli. However, as the resistance to the specific stress is built up during the stage of resistance, the organism becomes less capable of coping with extraneous stresses and may easily succumb to them. Thus an animal that has been treated with Morphine will succumb more readily to cold, atropine, or adrenaline. Exposure to cold or muscular activity will make the animal less resistant to other shock stimulus situations. Starvation, morphine poisoning, diphtheria toxins, and living in overheated quarters are likely to make the organism more susceptible to infections of the type encountered in common colds and pneumonia. It is a common medical observation that a patient recovering from a disease is likely, in building up a resistance to it, to become more susceptible to infections of various sorts and other complications. It would appear, therefore, that the organism possesses only a limited capacity to meet traumatic situations. If the homeostatic mechanisms are used to cope constantly with one situation, they become less able to cope with additional stresses.